Typically, a chopper type voltage comparator includes one or more inverter stages with signals coupled to the inputs thereof by coupling capacitors and three or four switches, generally of the transmission gate type. The transmission gates are used to supply an input signal and at least one reference signal to an input node of the comparator and to supply a feedback signal around one or two of the inverters. If the comparator is to be used in an analog-to-digital converter, it must be integrated into a single circuit on a semiconductor chip and to do this integration some type of semiconductor switches, such as the transmission gates, must be used.
The major problem with any of the semiconductor switches, and especially transmission gates, is the parasitic capacitance between the input/output terminals and the control terminals. The parasitic capacitance has a tendency to feed portions of the control signals from the control terminals to the input/output terminals, especially at very high frequencies. This problem can cause serious errors in analog-to-digital converters especially when the input and reference voltages are very small or the comparison becomes extremely close.